This invention relates generally to the fabrication of integrated circuits and, particularly, to photoresist utilized in the manufacturing of integrated circuits.
A thin photoresist film is patterned and used as a sacrificial layer to transfer the pattern to the underlying substrate during the manufacturing of integrated circuits. Patterns are created in a photoresist film as a result of exposure to radiation through a mask. The radiation causes a chemical reaction that changes the solubility of the photoresist. As a result, upon subsequent exposure to a developer solution, some of the photoresist may remain and other of the photoresist may be removed resulting in the transfer of a pattern from the exposure mask to the semiconductor structure.
This pattern, now resident in the photoresist structure, may in turn be utilized as a mask to remove portions of the underlying semiconductor structure using chemical etching processes. Thus, the use of photoresist enables the repeated fabrication of a large number of integrated circuits using a single mask that repeatedly transfers the same pattern to the semiconductor structure.
It has been the goal for many years in semiconductor fabrication to reduce the size of the features that are fabricated. Smaller integrated circuits generally mean faster integrated circuits and lower cost integrated circuits. One way to reduce the feature size is to use improved lithography. Generally, lithography improvements have been the result of changing the wavelength of the radiation used to expose the pattern. With wavelengths that are able to define even smaller patterns, the photoresist technology will also need to be improved to realize a decreased feature size. Namely, when smaller features may be exposed through improvements in lithography, it is also necessary that the photoresist be able to define the smaller features enabled by improved lithography.
The size of the features that undergo dissolution in the photoresist ultimately limits the line edge roughness (LER) and resolution that is available with any lithographic system. Line edge roughness is the roughness of the edge of the photoresist. This roughness is transferred to the underlying semiconductor structure in the subsequent processing steps, adversely affecting device performance. Thus, many manufacturers of integrated circuits have focused on reducing the molecular weight of the polymers used in photoresist in order to reduce line edge roughness and increase resolution.
Unfortunately, a reduction of molecular weight of these photoresist forming polymers may have a negative impact on the mechanical properties of the photoresist. For example, lower molecular weight photoresists may be more likely to exhibit photoresist pattern collapse. Obviously, when the pattern collapses, the photoresist may be non-functional.
Thus, there is a need for better photoresists that exhibit desirable line edge roughness and improved resolution, without resist photoresist pattern collapse at relatively high resolution radiation wavelengths, such as extreme ultraviolet (EUV) or 157 nanometers.